Abstract
ObjectiveTo investigate the pathophysiology of visual snow (VS), through a combined functional neuroimaging and magnetic resonance spectroscopy (1H‐MRS) approach.MethodsWe applied a functional MRI block‐design protocol studying the responses to a visual stimulation mimicking VS, in combination with 1H‐MRS over the right lingual gyrus, in 24 patients with VS compared to an equal number of age‐ and gender‐matched healthy controls.ResultsWe found reduced BOLD responses to the visual stimulus with respect to baseline in VS patients compared to controls, in the left (k = 291; P = 0.025; peak MNI coordinate [‐34 12 ‐6]) and right (k = 100; P = 0.003; peak MNI coordinate [44 14 ‐2]) anterior insula. Our spectroscopy analysis revealed a significant increase in lactate concentrations in patients with respect to controls (0.66 ± 0.9 mmol/L vs. 0.07 ± 0.2 mmol/L; P < 0.001) in the right lingual gyrus. In this area, there was a significant negative correlation between lactate concentrations and BOLD responses to visual stimulation (P = 0.004; r = −0.42), which was dependent on belonging to the patient group.InterpretationAs shown by our BOLD analysis, VS is characterized by a difference in bilateral insular responses to a visual stimulus mimicking VS itself, which could be due to disruptions within the salience network. Our results also suggest that patients with VS have a localized disturbance in extrastriate anaerobic metabolism, which may in turn cause a decreased metabolic reserve for the regular processing of visual stimuli.
Highlights
Visual snow (VS) is a neurological condition characterized by the constant, panfield perception of small flickering dots.[1]
We investigated cortical blood oxygenation leveldependent (BOLD) responses to visual stimulation in patients with VS syndrome compared to healthy volunteers, through the use of a functional magnetic resonance imaging experiment in which subjects were shown a visual task mimicking the effect of the “visual snow” itself
We studied the neurochemical properties of the lingual gyrus in VS patients, through proton magnetic resonance spectroscopy (1H-MRS)
Summary
Visual snow (VS) is a neurological condition characterized by the constant, panfield perception of small flickering dots.[1] In the VS syndrome, patients experience a combination of palinopsia, photophobia, entoptic phenomena, and nyctalopia.[2] VS constitutes a spectrum type disorder that can be worsened by its most common comorbidities, migraine, and tinnitus. Hallucinogenic persisting perceptual disorder[3,4] can sometimes mimic VS, the two are certainly separate conditions.[5]. VS pathophysiology is currently unknown; hypotheses include thalamo-cortical dysrhythmia of the visual pathways,[6] hyperexcitation of primary and secondary visual cortices,[7,8,9] increased saliency of normally ignored subcortical activity or perhaps a combination of all these mechanisms.[10] In particular, evidence for dysfunctional visual processing within the association cortices has emerged in a 2020 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals, Inc on behalf of American Neurological Association
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